A rotary-wing aircraft, or rotorcraft, generates lift utilizing rotor blades to propel a heavier-than-air flying machine through the air. Some examples of rotorcraft include helicopters, quad copters, etc. In some cases a cable may be coupled to the rotorcraft for transporting hanging loads. As the rotorcraft travels through the air, the payload at the end of the cable may swing in any direction. However, if the payload position is known relative to the position of the rotorcraft, the payload swing may be reduced utilizing small changes in the movement of the vehicle. It is desirable to minimize the swing of the payload because excessive movement may cause structural stress to the airframe of the rotorcraft and/or excessive power consumption in order to maintain control of the rotorcraft.
One approach for determining the position of the payload relative to the rotorcraft utilizes video camera(s) that capture digital images of the hanging load. The digital images may then be processed to determine the position of the payload relative to the rotorcraft. However, utilizing video cameras may fail in low visibility environments, such as fog, rain, dust, etc., when the payload cannot be visualized by the camera(s). Further, specialized visual markers may have to be applied to the payload in order to accurately locate the payload in the digitized images. When the markers are forgotten, the system may fail with the result being excessive movement of the payload.
Another approach for determining the position of the payload relative to the rotorcraft utilizes an inverted joystick approach. A ball joint is mounted to the rotorcraft and a cable extends from the ball joint to the payload. The ball joint includes a number of sensors that measure the position of the ball joint. The movement of the payload may then be measured utilizing the sensors. However, in this case the ball joint is subject to the full weight of the payload, which may be hundreds or thousands of pounds. This may result in a ball joint having a significant size and weight in order to support the weight of the payload, which also adds weight to the rotorcraft. Further, the complexity of the sensors used to measure the orientation of the ball joint may render the system more prone to failure.
It therefore remains a problem to measure the movement of hanging loads for rotorcraft in a manner that is reliable within a variety of flight environments without excessive complexity and/or added weight to the rotorcraft.